Centerless grinding machine



March 9, 1937.

A. G. BELDEN ET AL CENTERLESS GRINDING MACHINE Filed Jan. 25, 1935 2 Sheets-Sheet 1 INVENTORS ALBERT G. BELDEN RAYMOND/4. COLE p/$16 EY March 9, 1937. A. G. BELDEN ET AL GENTERLESS GRINDING MACHINE Filed Jan. 23, 1935 2 Shets-Sheet 2 M 5: 2 LM\WH| a M W Z? h I WOO i INVENTORS ALBERT G. BEL DEN RAYMOND A. COLE ATTOR Y Patented Mar. 9, 1937 UNITED sT 'rEs PATENT OFFICE ter, Mass.,

assignors to Norton Company,

Worcester, Mass., a corporation of Massachusetts Application January 23, 1935, Serial No. 3,022

22 Claims. (Cl. 51-103) The invention relates to grinding machines particularly of the so-called centerless type.

One object of the invention is to provide a centerless' grinder which, so far as stopping the action when the work-piece arrives at finished size is concerned, is self-acting orautomatic. Another object of the invention is to provide a centerless grinder of great precision, adapted to produce finished work-pieces varying from each other in diameter by a tolerance amount of very small dimensions. Another object of the-invention is to provide an apparatus in which the advantages of ready loading and high production of the centerless grinding principle and the advantages of close tolerance automatically attained are both or all of them achieved. Other objects will be inpart obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements,

and arrangements of parts as will be exemplified in the structure to be hereinafter described, and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawings, in which is shown one of various possible embodiments of the mechanical features of this invention,

Figure 1 is a front elevation of a grinding machine embodying the invention, the left-hand part of the frontframe member being broken away to show certain feed slide actuating mechanism;

Figure 2 is an enlarged view showing the grinding and regulating wheels and the sizing 'or gauging mechanism in cross-section;

Figure 3 is a horizontal sectional view taken mounted on a feed slide I2 is a grinding wheel it. Both the regulating wheel II and the grinding vwheel I3 may be abrasive wheels in which abrasive grain such as of alumina (A1203) or silicon carbide (S10) is bonded with a suitable bond, as a vitrified bond, or a resinous bond, in-

cluding shellac and phenolic condensation prod-' ucts, or rubber. The particular wheels will be chosen with due regard to the material of the work-piece and the type of finish to be imparted thereto, and the regulating wheel ll preferably has a denser structure than the grinding wheel l3, and so far as the features of this invention are concerned the regulating wheel ll may be other than an abrasive wheel, and any substance or rotary tool which will cut may be used for the wheel II. I

Preferably the abrasive wheel I3 is driven at a high peripheral velocity in the direction "of the arrow thereon, Figure 1, and preferably the regulating wheel II is driven at a relatively low peripheral velocity, in the direction of the arrow thereon, Figure 1.

Referring now to Figures 1 and 2, the wheel II is formed in two sections Ila and llb which, from the manufacturing standpoint, may be separate wheels or articles in the first instance. We desire to provide a space between elements of theregulating wheel II in which certain parts of our gauging instrumentality, hereinafter described, may be located, and we may provide this" space by forming a groove in an integral wheel II,-or as'illustrated in Figure 3 we may provide separate-independent wheel sections Ila and Ill) united together as illustrated in Figure 3 and as now to be described for the preferred embodiment of the invention. As illustrated in Figure 3, the wheel-or wheel section Ila has a lead center Ila while the wheel or wheel section llb has a lead center Ilb. We provide a sleeve I! having a tapered bore, a flange l8 at one end, and screw threads II at the other end. The outside of the sleeve II is cylindrical, and upon it we place the wheels Ila and llb, the lead centers Ila and llb Just fitting the sleeve II. Between the lead centers Ila and l lb we place a spacer ring III. A

washer I9 and a pair of nuts 20-20 whose threads fit the threads ll of the sleeve I! complete the assembly, the lead center I lb being held against the flange l8, and the lead center Ila being held in position by the washer l9 and nuts 20, which maybe tightened, with the spacer I8 interposed 'between the lead centers Ila and Ilb. Thusis formed a unit comprising two wheel sections Ila and llb which, in this embodiment of the invntion, are of the same diameter. While the, wheel sections Ila and Ill: need'not be of the same thickness, we have shown them so, and in that way they are-interchangeable.

The entire unit just described, including the sleeve I! and the wheel sections Ila and llb, we mount upon the tapered end 2| of a wheel spindle 22, the taperedbore of the sleeve l5 fitting the taper of the end 2|. 'I'he spindle 22 has a. threaded end 23 adapted to receive a couple of nuts Il-il and by tightening these we afllx wheel unit upon the tapered portion 2| of the spindle 22.

Referring now to Figures 1, 2 and 3, uprising from the machine base l0 we provide a wheel mounting 25 and in this wheel mounting 25 we locate a journal 26 which journals the spindle 22. As indicated in dotted lines on Figure l, the wheel spindle 22 has a pulley 21 on its rear end and this is connected by means of a belt 28 with a pulley 29 in or on the machine base. The pulley 29 may be driven from any source of power desired and is driven at a rate to impart the speed heretofore defined to the wheel Referring again to Figure 2, the wheel l3 which is the grinding or cutting wheel may be an integral piece, and desirably it has a lead center 38. We provide a sleeve 3| having a tapered bore, with a flange 32' at one end and a screw threaded portion 33 at the other end. By means of a washer 34 and a pair of nuts 35 the wheel I3 is mounted upon the sleeve 3|, and the unit may be mounted upon a spindle 36 having a tapered portion 31 by means of a pair of nuts 38 and a threaded portion 39 of the spindle 36, the construction in this respect being similar to that already described in connection with the wheel Referring particularly to Figure 1, we provide a wheel mounting 40 extending upwardly from the slide i2 and, referring to Figure 3, this wheel mounting supports a journal 4| which journals the spindle 36. Referring again to Figure 1, at the rear of the spindle 36 we provide a pulley 42 which may be driven by a belt 43 from a pulley 44 on a shaft 45. Pulley 44 and shaft 45 are, the same as pulley 29, to be considered as prime movers, and may themselves be driven from any suitable source of power, the rate and direction of rotation being determined in accordance with considerations previously stated, that is so as to drive the grinding or cutting wheel l3 at a relatively high speed so far as its peripheral velocity is concerned. From the shaft 45 we actuate the in and out feeding of the wheel l3 by movement of the feeding slide |2 as will now be described. We note that the arrangement shown in Figure 1 may be used despite the motion of the slide i2, for the actual distance that this slide travels may be very short in comparison with the distance between pulleys 42 and 44, and also the translation of the slide is in a line perpendicular to the plane connecting the axes of these pulleys, and belts, particularly leather belts, are known to have considerable elasticity.

Referring now to Figure l, fastened to the shaft 45 is a beveled gear 58 which mesheswith a beveled gear 5| which in turn is fastened to a shaft 52 that projects from a gear box shown in section in Figure 1 the side frame members of which are designated by the numerals 53 and 54. The shaft 52 is journaled in each of these side frame members which likewise journal shafts 55, 56 and 51, all of these shafts being, in this embodiment of the invention, parallel to each other. and collectively mounting reduction gearing and reversing mechanism. Still considering Figure l, and remembering that shaft 52 is constantly driven by means of the beveled gearing described, and noting that the direction of rotation is indicated by the arrow in Figure l, a spur gear 58 is fastened to the shaft 52 which meshes with and drives a spur gear 59 that is revoluble on the shaft 55. The spur gear 59 meshes with a spur gear 60 revoluble 'on the shaft 56; a spur gear 6| is attached to the spur gear 66 and the former meshes with a spur gear 62 that is attached to a spur gear 63, the unit 62, 63 being mountedon the shaft 51. The gear 63 meshes with a gear 64 which is mounted on a stud 65 projecting from a separate bracket 66. The gear 64 meshes with a gear 61 which is connected to a gear 68, the unit gears 61 and 68 being revolubly mounted on the shaft 56. Suitable spacing collars are provided as illustrated, and the train of gear described greatly decreases the angular velocity of a final gear 69 which, the same as gear 59, is revolubly mounted on the shaft 55. The direction of rotation of the gears is indicated by arrows in Figure 1. Thus the gear 59 rotates in one direction, while the gear 69 rotates in the other direction at but a fraction of the angular velocity of the gear 59. By securing the shaft 55 to one or the other of the gears 59 or 69, or by unclutching it from both of them, the shaft 55 may be driven in one direction with a high angular velocity, or in the other direction with a low angular velocity, or stopped altogether, and the clutching mechanism will now be described.

Mounted on the shaft 55 and connected to it by a sliding keyway or the like so that it shall revolve in unison with the shaft 55 but be translatable thereon, is a double faced clutch member 10 having a groove 1| into which projects a pair of pins 12 (only one shown) on the forked end of a lever 13 which is pivotally mounted on a shaft or stud 14 projecting from the machine base In. The gear 59 has clutch teeth 15 facing to the right, while the gear 69 has clutch teeth 16 facing to the left, which are shown in engagement with the right-hand clutch teeth of the clutch member 10. In this position of the parts, power is transmitted through the reduction gearing described to drive the shaft 55 slowly in what we may call the feed direction. When, by shifting the lever 13, the left-hand clutch teeth of the clutch member 10 are caused to engage with the right-hand clutch teeth 15 of the gear 59, the shaft 55 is driven rapidly in the opposite or, as we may call it, withdrawal direction.

Still referring to Figure I, mounted on the end of the shaft 55 is a beveled gear which meshes with a beveled gear 8| onthe lower end of a vertical shaft 82 that is supported by journals 83 and 84 attached to the machine base II]. On the upper end of the shaft 82 is a beveled gear 85 meshing with a beveled gear 86 loosely mounted on a screw shaft 81. Beveled gear 86 has a long hub 88 on the right-hand end of which are clutch teeth 89 adapted to mesh with clutch teeth 99 on a member 9|. The member 9| is keyed to the shaft 81 but is translatable thereon, and can be controlled by means of a plunger rod 92 with handle 93 projecting from a hand wheel 94 located on the left-hand side of the machine as shown in Figure 1. The hub 88 is journaled in a journal 95 which, together with journal 96 in the machine base I0, serves to support the screw shaft 61.

By means of the knob 93 on the end of the plunger rod 92 the screw shaft 81 can be clutched to the gear 86 or disconnected therefrom. In the former event the prime mover acting through the transmission described actuates the screw shaft 81; in the latter event it may be actuated by the hand wheel 94. The screw shaft 81 has feed slide translating screw threads cut therein at the right-hand'portion thereof, as indicated in Figure 1, and this portion of the screw shaft 61 passes through a nut 98 fastened to the underside of .the

slide |2 so that rotation of the shaft 91 translates v the slide I2. The slide l2 preferably is carried on V and flat ways, not shown, such being well known in practically all the machine tool industries and having been used previously in grinding machines. The screw shaft 81 is held from translation by a thrust bearing, which might be the bearing 90 or may be a separate bearing, not shown.

Still referring to Figure l, projecting from the front of the base I is a hood I00 of substantial strength and rigidity, which may be of the shape shown, and which provides a horizontal surface upon which to mountthe steady rest, and which provides another horizontal surface upon which to mount the gauging apparatus. The hood I00 also may serve to collect coolant which is discharged upon the work-piece as the grinding takes place, and it may act as a wheel guard to protect the operator from injury should either of the wheels explode, or comply with rules and regulations of competent governmental authorities for the guarding of rapidly rotating wheels. Extending upwardly from the inside lower plane surface of the guard I00 is a standard I0-I to which, as better shown in Figure 2, is fastened a steady rest I02 by means of bolt I03. The upper part of the steady rest I02 is forked as in-' dicated by showing it in elevation in Figure 2, the lower part being cross-sectioned to show that it is solid. The steady rest I02 has a pair of work-piece supporting surfaces I04 which are inclined upwardly to the left as viewed. in Figure 2, whereby the work-piece is supported by a surface tangent to it on a line somewhere in the neighborhood of 45 degrees removed from the line of tangency between the work-piece and the grinding wheel I3.

The work sizing or gauging device may be similar to that disclosed in our United States Patent No. 1,911,552 granted May 30, 1933, and in this specific embodiment of our present invention we illustrate and describe elements of our patented gauging device; and the description herein may be supplementediby reference to the above-numbered patent. The gauging elements of our sizing device fit in the space between regulating wheel sections Na and Ill) and in the space between the forks of the upper forked portion of the steady rest I02, desirably the latter space being equal in width to the former space.

Referring now to Figure 2, we provide an L- shaped casing I having a calipering head I08 which has a pair of adjustable contact screws I01 and I08 and a vertically movable plunger I09 as described in the aforesaid patent. We also provide bell cranlfleverd I0 mounted on a stud III together with adjustable contact elements I I2 and.

, low voltage electric energy as disclosed in the wiring diagram of Figure 4, while contact element I I2 is connected to a relay- I I5 and the contact element I I3 is connected to relay Hi. We prefer to use the relays and solenoids as disclosed in our patent, and in the operation of the calipering device an electric circuit is first completed through the contact element II2, and thereafter through the contact element II3, energizing first the relay H5 and thereafter the relay II6. Re-' ferring now to Figure 4 the relay Il5, when shown.

energized, causes high voltage or high power current'to energize a solenoid I I1, while the relay II 6 causes energization of a solenoid II8. Thecircuits will be perfectly clear from inspection of Figure 1, and furthermore are described in the aforesaid patent, and therefore we have refrained from giving every wire a reference character. As

in the disclosure of the aforesaid patent, we

outwardly. As disclosed in the, aforesaid patent,

in a grinding machine which lstaking a fairly heavy cut, stopping of the in-feed does not terminate the grinding, because the machine parts are under some tension and act asa spring with respect to the very close tolerances involved in precision grinding, and hence grinding" proceeds even after the feed is stopped, and this phenomenon is known as sparking out". grinding of work-pieces to exact size we propose to' reduce the work-pieces in diameter to a dimension somewhat above the desired'finished size and at that time to stop the in-feed; the remainder of the grinding is a finishing'or sparking out operation and when the work-piece comes to the exact desired size (exact within very close limits) the feed slide I2 runs out pursuant to closing of the contact between bell crank H0 and contact element H3, and grinding and-finishing thereby definitely cease. As in the aforesaid patent, low

voltage energy is used for thecircuits involving the actual contact e1ements,thus avoiding pitting and arcing as much as possible, while high power circuits are used to energize the solenoids H1, H8 thus obtaining a strong and positive action, and this is made possible by the use of the relays II, IIO.

We support the'gauging or calipering mechanism from the upper part of the hood I00. As shown in Figure 2, a clamping device I20 adjustably holds the casing I05 from falling below a certain limit supposing there is no work-piece in the head I06. The casing I05 extends through an opening I2I in. the hood I00 which is oversize, and a spring I22 extending between the clamp I20 and a post I23 urges the casing I05 clockwise, thus to maintain the screw I0'I- in contact with the work-piece and furthermore in order to carry the work-piece-away from the regulating wheel II when the carriage I2 runs out. -A stop arm I24, above the spring I22, acts, with the spring to exert a couple upon the casing I05. There is a limitto possible angular motion of the casing I05, determined by the size of the opening I2I. and the amplitude may be varied by means of adjustment screws or the like, not

Referring now to Figure 1', the lever I3 which controls the motion of' the carriage I2 has, as previously stated. three positions, the middle position being the neutral-position, the left-hand position being the feed position wherein the slide I2 moves to the right, and the right-hand position being the rapidwithdraw'al position, wherein the slide I2 moves outward rapidly. We provide a three-position cam I20 acted upon by a spring I detent I26, so that the lever I3 may be heldin anyone of its three positions, and urged into any one of them when the various high points of 'the.

cam I20 have been passed by the dagger portion of the detent I20, and for convenience this ca m For centerless I has been marked RNF which letters respectively mean reverse, neutral and feed. In order to stop the reverse or outward movement of the slide I2, attached to it is a downwardly extending rigid arm I carrying an adjustable contact rod I3I which is in line with the upper part of the lever 13.

Referring now to Figures 1 and 4, the solenoids I I1 and H8 operate the lever 13 in the following manner: The upper part of lever 13 has a laterally extending pin I32 engaging a spool I33 on a solenoid rod I34 which is made of magnetic and non-magnetic material attached together in such manner that energization of either solenoid II'I, IIB urges the solenoid core rod I34 to the right. Assuming the lever 13 is in its left-hand position as shown in Figure 1, and remembering that the solenoid I I1 is first energized, this action as stated draws the rod I34 to the right. on the right-hand end of rod I34 is an upwardly extending projection I35 in position to strike an in-' clined member I36 attached to a switch arm I31 which, as shown in Figure 4, is in circuit between the solenoid N1, the relay H5, and the high voltage power lines. Thus as the rod .I34 is drawn to the right, and as the detent I26 drops into neutral position, the circuit through solenoid IE1 is broken and feed of the slide I2 is stopped.

Assuming now the lever 13 is in central or neutrol position, grinding nevertheless continues as described, until the final contact is made through the contact element I I3, energizing the relay II6, which in turn energizes the'solenoid '8, and again urges the core member,l34 to the right thus moving the lever 13 to its right-hand or reverse position and causing the slide I2 to run outwardly. As the dagger part of the detent I26 drops into the reverse notch of the cam I25, an upwardly extending projection I40 carried by the left-hand end of the solenoid rod I34 strikes an inclined member I4I on a switch arm I42 which is'i n" circuit between solenoid II8, relay H6 and the power line, shown in Figure 4, and thus this circuit is opened. The slide I2 continues out- 45wardly until the rod I3I strikes the lever 13,

which action forces this lever into neutral position. Preferably the switch arm I31 is loosely pivoted so that, when starting up the machine again, the moment the lever 13 is returned to feed position the circuit'at this switch will be closed, but preferably the switch arm I42 is mounted on a friction pivot so that it will remain open despite the fact that member I40 has left the inclined member MI, in order to save useless energization of the solenoid II8. In order to close this switch 'I42 again when a new grinding operation is commenced, we provide a projection I45 on the lever 13 adapted to engage an upwardly extending arm I46 of the switch member I42 when the lever 13 is pulled to the left. The lever 13 is preferably keyed to its pivot shaft 14, so that by means of a lever I50 onthe front or back of the machine the transmission may be controlled.

Assuming that the operator finds the machine with the grinding whe'el I3 withdrawn from the work-piece and the lever 13 in mid or neutral position, after adjusting the calipering device for a particular -size of work-piece, the operator raises the plunger I09, as by means of a pin I5I Figure 2, and inserts a. work-piece between the screws I01, I08 and the plunger I09. The weight of the casing I05 positions the work-piece against the surfaces I04 of the steady rest I02, and, as-

" 7 'suming the regulating wheel II is rotating, the

the casing I05, and actually urges the screw I08 upwardly. When the contact is made at contact element I I2 as described, the lever 13 is shifted to neutral position as already set forth and the finish grinding proceeds until the desired size is reached, whereupon the slide I2 runs out and stops. The spring I22 carries the work-piece away from the regulating wheel or at least removes the pressure between these elements as soon as the wheel I3 runs out, but at all events the work-piece cannot follow wheel I3 on account of the limits of the opening I2I. With the wheel I3 out of the way the operator can replace the finished work-piece with an unfinished one and, by merely shifting the control lever I50, cause the machine to resume grinding. The shape of. the steady rest I02 has been chosen to insure grinding of work-pieces to a true cylindrical form, properly supporting the thrust of the grinding wheel, and the thrust of the screw I01 is opposed to the thrust of the grinding wheel.

It will thus be seen that there has been provided by this invention an apparatus in which the various objects hereinabove set forth, together with many practical advantages, are successfully achieved. As many possible embodi-' ments may be made of the above invention, and as many changes might be made in the embodiment above set forth, it is to be understood that all matter as hereinbefore set forth and as shown in the accompanying drawings is to be interpreted as illustrative arid not in a limiting sense. I

i. In an external centerless grinding machine, a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a regulating wheel, a steady rest, a calipering device formed to contact the exterior surface of a work piece, and

means operated thereby to cause a grinding operation to determine and cease when the work piece comes to the desired finished size.

2. In' an external centerless grinding machine, a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a regulating wheel, a, work rest, a calipering device formed to contact the exterior surface of a work piece, a feeding mechanism to move relatively the grinding wheel and regulating wheel, and means controlled by the calipering device to arrest the movement of said feeding mechanism.

3. In a grinding machine, a work throat comprising a grinding wheel, a regulating wheel and a work rest, and precision means comprising a calipering device contacting the work at opposite ends of a diameter to regulate the amount of material removed from the work-piece.

4. In an external centerless grinding machine, a. grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a regulating wheel, a wheel slide for one of said wheels, translation means to move said slide, a support for the work piece, and work piece exterior contacting calipering means to arrest the movement of the slide wheel slide for one of said wheels, translation means to move said slide, a support for the work piece, a calipering device formed to contact the exterior surface of a work piece, and means actuated by said calipering device to cause the translation means to separate said wheels when the work piece reaches a certain size.

6. In a grinding machine, a grinding wheel, a regulating wheel, a steady rest, a wheel slide, translation means including a feed train to move said slide, a quick traverse train to withdraw said slide, clutching and reversing mechanisms to select one or the other of said trains and having a neutral position, and precision means automatically actuating said last-named mechanisms.

7. In a grinding machine, a grinding wheel, a regulating wheel, a slide arranged to move said grinding wheel with respect to a work-piece, a precision device to measure the size of the workpiece, a transmission mechanism including afeed train and a quick movement train to move said slide, clutching and reversing mechanism for said transmission, and means controlled by said precision means to actuate said clutching and reversing mechanism.

8. In a grinding machine, a grinding wheel, a regulating wheel, a work contacting caliper, a lever controlled by said caliper, a contact element adapted to close a circuit when said lever moves, a relay energized when said circuit is closed, a solenoid controlled by said relay, a clutch element actuated by said solenoid, a quick withdrawal transmission train controlled by said clutch element, and a slide carrying one of said wheels and moved by said transmission.

9. In a grinding machine, a work contacting calipering device, a grinding wheel, and a twopart regulating wheel between the elements of which said work contacting calipering device is located.

10. In a. grinding machine, apair of wheels on parallel axes, there'being a groove in one wheel and a calipering device located in said groove.

11. In a grinding machine, three wheels, two of them mounted coaxially and the third on an axis parallel to the axis of the first two, and a calipering instrumentality mounted between the wheels, which are coaxial.

12. In a. grinding machine, a grinding wheel having a grinding face, a work rest substantially as long as said face except for a cut-out intermediate the ends of the grinding face, and a calipering device located in said cut-out.

13. In a grinding machine, a grinding wheel having a grinding face, a regulating wheel having a face substantially conterminous with the grinding face except for a cut-out intermediate its ends, and a work calipering device located in 60. said cut-out.

having opposed peripheries substantially con-- terminous except for a cut-out in one of them, a work rest having a cut-out substantially. conterminous with the first mentioned cut-out, and a calipering device located in said cut-outs.

16. In an external centerless grinding machine,

I a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a regulating wheel, feeding means to feed one of said wheels towards the other one, a calipering device formed to contact the exterior surface of a work piece and therefore not affected by wear on said wheels, and means operated thereby to cause the grinding operation to cease.

17. In an external centerless grinding machine, a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a regulating wheel, a

.work rest, said wheels and rest being so aligned that the work piece is rotated in a flxed position and ground, and work exterior contacting calipering means to cause the grinding to proceed until the work reaches a predetermined size and then to cause the grinding to cease.

18. In a centerless grinding machine, a grinding wheel, a regulating wheel, a work rest, means to cause said wheels to approach each other, reversing means for said last named means which when actuated causes the wheels to recede from each other, and work contacting calipering means to actuate said reversing means when the workpiece has reached a predetermined size.

19. In an external centerless grinding machine, a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a: regulating wheel, means to hold a work piece in fixed position between said wheels, means to cause said wheels to approach each other, and means to arrest the approaching movement when the work piece reaches a predetermined size.

20. In an external centerless grinding machine, a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground by the machine, a regulating wheel, means to hold a work piece in fixed position between said wheels, means to cause said wheels to approach each other, and calipering means contacting the exterior of the work to cause said wheels to part when the work piece reaches a predetermined size.

, 21. In an external centerless grinding machine, a grinding wheel having a diameter greater than that of the largest work piece adapted to be ground on the machine, a regulating wheel, means to hold a work piece in fixed position between said wheels, means to cause said wheels to approach each other, and calipering means located in the area defined by said grinding wheel and regulating wheel for arresting the means to cause said wheels to approach each other.

22. In an external centerless grinding machine, a grinding, wheel having a diameter greater than the largest work piecmadapted to be ground by the machine, a regulating wheel having a diameter greater than the largest work piece adapted to be ground by-the machine, a steady rest between said wheels and forming with them a. grinding throat, a mounting for one of said wheels permitting it to be moved towards the other one to effect a plunge-cut grinding operation. and work size determining means to control the exterior diameter of the work piece irrespective of wear or reduction in diameter of either one of the wheels, said work size determining means acting during the actual grinding operation.

ALBERT G. BELDEN.

RAYMOND A. COLE. 

